We first describe the structure of a general multiple antenna OFDM communication system.
FIG. 1 illustrates the structures of transmitting and receiving ends using a single codeword (SCW) in a general multiple antenna OFDM communication system and FIG. 2 illustrates the structures of transmitting and receiving ends using multiple codewords (MCW) in a general multiple antenna OFDM communication system.
As shown in FIGS. 1 and 2, a transmitting end 100 in a general multiple antenna OFDM communication system includes an encoder 101, an HARQ function module 102, a channel interleaver 103, a serial/parallel (S/P) converter 104, a mapper 105, a resource allocation module 106, an IFFT module 107, etc.
Specifically, the encoder 101 performs coding to insert extra bits to data bits in order to reduce channel or noise effects and the HARQ function module 102 performs retransmission and rate matching. The channel interleaver 103 shuffles, on a bit basis, bits with CRCs or the like inserted into the bits in order to spread an intensive burst error that may occur in a channel. The S/P converter 104 converts a serial signal into a parallel signal. The mapper 105 converts the parallel bit information into symbols. The resource allocation module 106 maps the symbols to appropriate subcarrier positions and the IFFT module 107 modulates them into OFDM symbols and transmits the OFDM symbols over a channel 300.
Since the transmitting end 100 of FIG. 1 uses a single codeword, the transmitting end 100 of FIG. 1 includes one encoder 101, one HARQ function module 102, and one channel interleaver 103 as shown in FIG. 1. On the other hand, since the transmitting end 100 of FIG. 2 uses two codewords, the transmitting end 100 of FIG. 2 includes two encoders 101, two HARQ function modules 102, and two channel interleavers 103 as shown in FIG. 2.
As shown in FIGS. 1 and 2, the receiving end 200 may include an FFT module 201, a resource deallocation module 202, a demapper 203, a parallel/serial (P/S) converter 204, a channel deinterleaver 205, an HARQ defunction module 206, and a decoder 207. The receiving end 200 receives a signal and performs the reverse of the procedure of the transmitting end 100.
Specifically, in the receiving end 200, data, which has passed through the channel 300, is extracted from the physical channel through the FFT module 201 and the resource deallocation module 202. Then, the symbol information is converted into bit information through the demapper 203. The bit information then passes through the P/S converter 204 and the channel deinterleaver 205, and the coding rate is converted back to a coding rate for decoding at the HARQ defunction module 206 and is then input to the decoder 207. Finally, the decoder 207 estimates data bits.
Thereafter, through an error detection code such as a CRC bit, it is determined whether or not an error occurred in the transmission packet. The receiving end 200 returns a NACK signal to the transmitting end 100 if it is determined that an error occurred and returns an ACK signal to the transmitting end 100 if it is determined that no error occurred. The transmitting end 100 does not retransmit data when the ACK signal is received and retransmits data in the order specified by a scheduler when the NACK signal is received.
The following is a more detailed description of the function of the resource allocation module 106 that is involved in data retransmission in the HARQ function in the structures of the transmitting and receiving ends 100 and 200 described above with reference to FIGS. 1 and 2 in association with the data retransmission method.
FIG. 3 illustrates a conventional method in which a resource allocation module maps data to multiple antennas to retransmit the data through the multiple antennas.
As shown in FIG. 3, in the conventional retransmission method, a packet is retransmitted through the same antenna as that through which the packet was previously transmitted. Here, a subcarrier location to which the packet data is allocated can be changed or unchanged.
If data is transmitted at each retransmission through the same antenna as that through which the data was previously transmitted in the above manner, the data is transmitted over a channel similar to that over which the data was previously transmitted and taking full use of channel diversity gain is difficult. That is, if data is retransmitted over a good channel at second transmission after being transmitted over a bad channel at first transmission, the retransmission partially compensates for a reduction in the performance due to the bad channel. However, if data is retransmitted through the same antenna as during first transmission, it is difficult to achieve channel diversity gain.